CN115557881B - Organic small molecule hole transport material, synthesis method and application thereof - Google Patents

Abstract

The invention discloses an organic small molecule hole transport material, a synthesis method and an application thereof. The hole transport material uses tri(4-iodophenyl)amine as a central core, introduces a modified capped carbazole group, has a simple molecular structure, has an adjustable and suitable energy level position, a high hole mobility and conductivity, and exhibits good solubility in organic solvents. The hole transport material is applied to the hole transport material in quantum dot (including perovskite quantum dots and other core-shell quantum dots) electroluminescent diodes, and the resulting device exhibits uniform luminescence, low turn-on voltage, high luminous efficiency and good life stability, and has broad application prospects.

Description

Organic small molecule hole transport material, synthesis method and application thereof

Technical Field

The invention relates to the field of quantum dot light-emitting diode materials, in particular to carbazole group-modified organic small molecule hole transport materials and applications thereof in quantum dot light-emitting diodes.

Background Art

The structure of quantum dot light-emitting diode (QLED) is usually a double heterojunction structure with a sandwich structure, with wide bandgap p-type and n-type semiconductors as hole transport layer (HTL) and electron transport layer (ETL), respectively, and narrow bandgap semiconductor as light-emitting layer. During the operation of QLED, holes and electrons are injected into the light-emitting layer from HTL and ETL, respectively. Then, photons are generated and emitted out of the device through the radiative recombination of electron-hole pairs in the quantum dot light-emitting layer. In this process, QLED currently still has problems such as large carrier injection barrier and unbalanced carrier mobility. The existence of these problems directly leads to high device start-up voltage, difficulty in reaching the theoretical limit of luminous efficiency, and insufficient device stability. Therefore, it would be an effective strategy to develop a new hole transport layer and adjust the energy level, hole mobility, etc. to optimize and improve device performance.

The hole transport layer that matches high-performance QLED needs to meet the following conditions: (1) It has a HOMO energy level that matches the adjacent functional layer, especially the light-emitting layer, to reduce the hole injection barrier in the device; (2) It has a shallow LUMO energy level to reduce the carrier loss caused by the escape of a small number of high-energy electrons from the barrier; (3) The absorption spectrum of the material should not overlap with the emission spectrum of the light-emitting layer as much as possible to prevent the loss of luminous efficiency caused by energy transfer between layers; (4) It has an appropriate conductivity with hole mobility so that holes and electrons can be injected into the device in a balanced manner; (5) When the solution method is used, it meets the requirements of orthogonal solvents to avoid the corrosion of the solvent on the lower film and the corrosion of the upper solvent; (6) It has good hydrophobicity, thermal stability and chemical stability, is not easy to absorb moisture and degrade, and is not easy to cause the quantum dot light-emitting layer to degrade due to contact, so as to achieve a longer device life.

Currently, there are relatively few hole transport layers used in QLEDs, which makes it relatively difficult to select matching hole transport materials from the available materials when designing the device. Therefore, the development of new hole transport materials will help make the device's luminous efficiency closer to the theoretical limit.

Summary of the invention

In order to improve the luminous efficiency of quantum dot light-emitting diodes, the present invention provides an organic small molecule hole transport material with 4,4',4"-tri(carbazole-9-yl)triphenylamine as the core and modified with carbazole side groups. The material can regulate the energy levels of the highest occupied orbital and the lowest unoccupied orbital of the molecule and the hole mobility by introducing different groups and different introduction positions. The material has good thermal stability, an energy level matching that of quantum dots, a high hole mobility, good solubility, and is easy to synthesize and purify. The material can be applied to quantum dot light-emitting diodes, and can also be expanded to the fields of perovskite light-emitting diodes, perovskite solar cells, organic solar cells, and organic electroluminescent devices.

The purpose of the present invention is achieved through the following technical solutions:

The carbazole group-modified organic small molecule hole transport material provided by the present invention has the following molecular structure formula (I):

Formula (I), wherein _R1 - _R8 are selected from any one of hydrogen atom, methoxyl group, phenoxyl group, methylmercapto group, phenylmercapto group and the like, and any 1-4 positions of R1-R8 are combined with different groups.

The method for preparing the carbazole group-modified organic small molecule hole transport material described in formula (I) comprises the following steps:

(1) a step of reacting triphenylamine and N-iodosuccinimide under the action of acetic acid as a catalyst to prepare tri(4-iodophenyl)amine,

(2) a step of subjecting tri(4-iodophenyl)amine and carbazole having different substituents to a Buchwald-Hartwig reaction to prepare a target product,

Preferably, in step (1), the reaction system uses chloroform as solvent.

Preferably, in step (1), the molar ratio of N-iodosuccinimide to triphenylamine is 3 to 4:1, preferably 4:1.

Preferably, in step (2), the reaction is carried out under a protective atmosphere, and the reaction system uses DMF as a solvent.

Preferably, in step (2), the reaction uses cuprous iodide, 1,10-phenanthroline and potassium carbonate as catalysts, the molar ratio of cuprous iodide to tri(4-iodophenyl)amine is 0.5-0.7:1, preferably 0.6:1; the molar ratio of 1,10-phenanthroline to tri(4-iodophenyl)amine is 0.5-0.7:1, preferably 0.6:1; the molar ratio of potassium carbonate to tri(4-iodophenyl)amine is 6-9:1, preferably 8:1.

Preferably, in step (2), the molar ratio of tri(4-iodophenyl)amine to the modified carbazole molecule is 1:4 to 4.5, preferably 1:4.

The present invention also proposes an application of the organic small molecule hole transport material as a hole transport material in a quantum dot light emitting diode.

Preferably, it is used as a hole transport material in a p-i-n structured quantum dot light emitting diode.

The present invention also proposes a use of the hole transport material as a light-emitting material in an organic electroluminescent device.

Compared with the prior art, the advantages of the technical solution of the present invention are as follows:

1. The series of organic small molecule hole transport materials modified with carbazole groups provided by the present invention have a simple molecular structure, with tri(4-iodophenyl)amine as the central core, and the introduction of modified carbazole molecules (with methoxy, phenoxy, methylmercapto, phenylmercapto and other groups), which have good photoelectric effect and are conducive to the preparation of high-performance light-emitting diodes. The introduction of different groups can effectively improve the energy level and hole mobility of the molecule, so that the material can have better hole injection and transport performance, reduce the turn-on voltage, improve device performance, improve luminous efficiency, and improve device stability.

2. The organic small molecule hole transport material modified with the carbazole group of the present invention, by introducing side chain groups, makes the material have good thermal stability, good hydrophobicity, suitable for solution method application, and meets the requirements of orthogonal solvents. At the same time, the interaction between the introduced group and its adjacent layer is conducive to achieving high performance in device applications.

3. The present invention applies the organic small molecule hole transport material modified by the carbazole group to the quantum dot light-emitting diode, which has a suitable energy level, a high hole mobility, and good hydrophobicity, can achieve a lower turn-on voltage and a higher luminous efficiency and brightness of the quantum dot light-emitting diode, and can also improve the device stability.

4. The material of the present invention can be preferentially used in the hole transport layer of quantum dot light-emitting diodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of a quantum dot light-emitting diode prepared using i-1 and i-2 as hole transport layers.

FIG. 2 shows the ultraviolet-visible absorption spectrum and fluorescence spectrum of the material i-1 prepared in an embodiment of the present invention after being prepared into a thin film.

FIG3 shows the ultraviolet-visible absorption spectrum and fluorescence spectrum of the material i-2 prepared in an embodiment of the present invention after being prepared into a thin film.

FIG. 4 is a current density-operating voltage-brightness relationship curve of a quantum dot light-emitting diode using i-1 and i-2 as hole transport materials according to the present invention.

FIG. 5 is a current efficiency-current density relationship curve of the quantum dot light-emitting diode using i-1 and i-2 as hole transport materials according to the present invention.

FIG. 6 is an electroluminescence spectrum diagram of a quantum dot light-emitting diode using i-1 and i-2 as hole transport materials according to the present invention.

FIG. 7 is a ¹ H NMR spectrum of material i-1 prepared in Example 1.

FIG8 is a ¹ H NMR spectrum of material i-2 prepared in Example 2.

DETAILED DESCRIPTION

The present invention will be explained below in conjunction with specific application examples and diagrams. The embodiments provided below will help researchers in the field to better understand the present invention, but are not limited to the present invention in any form. Based on the concept of the present invention, there may be several modified and replaced forms, which all belong to the protection scope of the present invention.

The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

The compounds synthesized by the present invention are characterized by UV-vis and PL spectra and nuclear magnetic resonance. At the same time, quantum dot light-emitting diodes are prepared using the synthesized materials as hole transport layers, and the performance of the devices is analyzed; the research finds that these devices have good performance.

The invention has a reasonable design, and the prepared organic small molecule hole transport material modified with a carbazole group has a simple molecular structure, with tri(4-iodophenyl)amine as the central core, and a modified end-capped carbazole group is introduced. The synthesis steps of this type of material are simple and easy to purify. It has good solubility in organic solvents, a suitable molecular energy level, and a high hole mobility. When it is applied to a quantum dot light-emitting diode, the device has good stability, a low start-up voltage, and high luminous brightness and luminous efficiency.

Example 1

A synthesis of an organic small molecule hole transport material i-1 modified with a carbazole group, the synthesis route is as follows:

(1) At room temperature, triphenylamine (3.68 g, 14.47 mmol), N-iodosuccinimide (10.8 g, 48 mmol) and chloroform (90 mL) were added to acetic acid (60 mL), stirred overnight, and protected from light with tin foil. The mixture was then poured into a saturated aqueous solution of sodium thiosulfate and extracted with dichloromethane to obtain an organic phase. The organic phase was concentrated to remove the solvent and crystallized from n-hexane-dichloromethane to obtain 8.7 g of tri(4-iodophenyl)amine.

(2) Tri(4-iodophenyl)amine (0.340 g, 0.55 mmol), 2,7-dimethoxycarbazole (0.50 g, 2.20 mmol), cuprous iodide (63 mg, 0.33 mmol), 1,10-phenanthroline (60 mg, 0.33 mmol), and potassium carbonate (0.61 mg, 4.42 mmol) were added to dry DMF (20 mL). The mixture was refluxed under argon protection, and the reaction was monitored by thin layer chromatography (TLC). After the reaction was completed, water was added to the reaction mixture, and the precipitate was filtered and washed with water and methanol several times. Purification by acetone crystallization gave 0.31 g of i-1 with a yield of 60%. The absorption and PL spectra are shown in FIG2 , and the NMR spectrum is shown in FIG7 . ¹ H NMR (400MHz, C ₆ D ₆ ,298K), δ (ppm): 7.91 (d, J = 8.6 Hz, 6H), 7.16 (m, 6H), 7.10 (m, 6H), 7.06 (d, J = 7.8 Hz, 6H), 6.98 (dd, J = 8.6 Hz, J = 2.1 Hz, 6H), 3.52 (18H, s, OMe). ¹³ C NMR (100MHz, C ₆ D ₆ , 298K), δ (ppm): 158.56, 145.70, 142.20, 132.46, 127.59, 124.81, 119.90, 117.38, 107.76, 94.21, 54.45.

Example 2

A synthesis of an organic small molecule hole transport material i-2 modified with a carbazole group, the synthesis route is as follows:

(1) At room temperature, triphenylamine (3.68 g, 14.47 mmol), N-iodosuccinimide (10.8 g, 48 mmol) and chloroform (90 mL) were added to acetic acid (60 mL), stirred overnight, and protected from light with tin foil. The mixture was then poured into a saturated aqueous solution of sodium thiosulfate and extracted with dichloromethane to obtain an organic phase. The organic phase was concentrated to remove the solvent and crystallized from n-hexane-dichloromethane to obtain 8.7 g of tri(4-iodophenyl)amine.

(2) Tri(4-iodophenyl)amine (0.340 g, 0.55 mmol), 3,6-dimethoxycarbazole (0.50 g, 2.20 mmol), cuprous iodide (63 mg, 0.33 mmol), 1,10-phenanthroline (60 mg, 0.33 mmol), and potassium carbonate (0.61 mg, 4.42 mmol) were added to dry DMF (20 mL). The mixture was refluxed under argon protection, and the reaction was monitored by thin layer chromatography (TLC). After the reaction was completed, water was added to the reaction mixture, and the precipitate was filtered and washed with water and methanol several times. Purification by acetone crystallization gave 0.88 g of i-2 with a yield of 62%. The absorption and PL spectra are shown in FIG3 , and the NMR spectrum is shown in FIG8 . ¹ H NMR (400MHz, DMSO-d ₆ ,298K), δ (ppm): 7.84 (m, 6H), 7.61 (d, J = 8.6Hz, 6H), 7.49 (d, J = 7.8Hz, 6H), 7.38 (d, J = 8.6Hz, 6H), 7.06 (d, J = 8.6Hz, 6H), 3.52 (18H, s,OMe). ¹³ C NMR (100MHz, DMSO-d ₆ ,298K), δ (ppm): 153.73, 145.45, 1342, 132.45, 127.59, 125.23, 123.15, 115.34, 110.58, 103.31, 54.88.

Application Example 3

The preparation process of quantum dot light-emitting diodes based on organic small molecule hole transport materials modified with carbazole groups.

The compounds of Example 1 (i-1) and Example 2 (i-2) are used as hole transport materials to prepare quantum dot light-emitting diodes. Figure 1 is a schematic diagram of the device structure, which adopts a p-i-n structure.

The device structure is ITO/PEDOT:PSS/i-1 or i-2/quantum dots/TPBi/LiF/Al

The device preparation method is as follows: ITO glass is ultrasonically washed with deionized water, ethanol, and acetone for 15 minutes, and then ITO is placed in a drying oven at 100°C for drying (1 hour), and UVO treated for 20 minutes before use. PEDOT:PSS is spin-coated at 4000rpm (60s) as a hole injection layer, and annealed at 150°C in air for 15 minutes. Transfer to a glove box with a nitrogen atmosphere. 5-15 mg of i-1 or i-2 is dissolved in 1 mL of chlorobenzene, stirred until clear, and then spin-coated on the PEDOT:PSS film at 2000rpm (60s) in the glove box, and annealed at 150°C for 15 minutes. After cooling, quantum dots are spin-coated at 2000rpm (60s). At a pressure of 4.0× ^10-4 Pa, 40nm of TPBi and 1nm of LiF are successively evaporated on the quantum dot layer by thermal evaporation, and finally a 100nm thick aluminum electrode is evaporated. This is the entire preparation process of quantum dot light-emitting diodes. The maximum effective area of the light-emitting diode is 0.09 ^cm2 .

The turn-on voltage, IVL curve and luminous efficiency of the prepared light-emitting diode were tested in air.

Figure 4 is the current density-voltage-luminous brightness curve of the light-emitting diode based on i-1 or i-2, and Figure 5 is the current efficiency-current density curve. The turn-on voltage of the best device is 2.75V, the luminous brightness is 12476.04cd/ ^m2 , and the current efficiency is 57.1cd/A. Figure 6 is the electroluminescence spectrum of the quantum dot light-emitting diodes with i-1 and i-2 as hole transport materials, and the electroluminescence spectra of the two are similar.

The above content describes the specific operational details of the present invention, but it is only for the purpose of clearly and completely presenting the application examples of the present invention, and does not limit the specific implementation methods. Researchers in this field can make various supplements or improvements within a certain range, which does not affect the essential content of the present invention. The final product synthesized in the present invention is not limited to the application in the field of quantum dot light-emitting diodes, but can also be applied to other fields such as perovskite light-emitting diodes, perovskite solar cells, organic solar cells and organic electroluminescent devices. Due to limited space, it will not be elaborated here, but a series of studies derived therefrom still belong to the scope of protection of the present invention.

Claims (2)

1. Application of an organic small molecule hole transport material modified by a carbazole group as a hole transport material in a quantum dot light-emitting diode, characterized in that the organic small molecule hole transport material modified by a carbazole group has the following structure: 2. The use as claimed in claim 1, characterized in that the organic small molecule hole transport material modified by carbazole group is used as a hole transport material in a quantum dot light-emitting diode with a p-i-n structure.